A motor is used as a drive device for converting electric energy in the industrial, household, and vehicle fields to a mechanical output. A claw-pole motor is used for an OA device, a vehicle device, and the like because of its low-cost structure and a simple drive circuit. Usually, the claw-pole motor is used as a two-phase stepping motor as described in Japanese laid-open Patent Application Publication No. H7-227075. Motors are generally classified into a single phase, two phases, and three phases, which are properly used according to uses. Among the motors, the three-phase motor has excellent controllability and has an advantage that it can be driven by using the small number of transistors.
Usually, as described in Japanese laid-open Patent Application Publication No. H7-227075, the material of a stator core in a claw-pole motor of this kind is a rolled steel plate of SPCC or the like. A claw pole part is formed by bending the plate, and a cylindrically-wound coil of stator is sandwiched by a pair of stator core blocks (halves).
Incidentally, if using SPCC as the stator core, an iron loss occurring in the stator core may be prone to become large because SPCC is comparatively inferior in magnetic property.
Furthermore since the SPCC for the stator core is bent into a final product, residual stress occurs in the bent part in the stator core, and the magnetic property further deteriorates due to distortion. Since the bent part is a part on which magnetic flux is particularly concentrated, a large iron loss occurs, and a low-efficient motor may be resulted. Additionally, as an inner side of such a magnetic pole core which is plastic-worked by bending has a cantilever structure, its circularity may be prone to become very low. Due to the influence of the low circularity, the motor may have large cogging torque. Under the present circumstances, the motor is employed for uses which do not require high efficiency, low torque pulsation, low vibration, low noise, and the like.
The present invention is to provide a multiphase claw-pole type electric rotary machine structure (for example, motor structure) capable of reducing cogging torque, and to provide a method of reducing the cogging torque in a multiphase claw-pole type motor with magnetic claw-poles made of a powder magnetic core. The claw-pole type electric rotary machine has a structure in which stator units in respective phases are independent of each other, and the positional relations of the independent phases is brought into move out of the designed relations due to an assembly error and the like. In a three-phase motor, their phases shift by 120° from one to another in electrical angle in the positional relations without assembly error. However, such shift slightly varies due to an error (deviation) which occurs at the time of assembly and the like, and cogging torque due to an error increases. The cycle of the cogging torque occurring due to an error is longer than that of cogging torque determined in designing, and the absolute value of the cogging torque is a few times or tens times as large as that determined in designing. The cogging torque exerts an influence upon torque ripples and smoothness of motor rotation and causes vibration and noise. It is desired to reduce the cogging torque, and the reduction of the cogging torque is an important theme in all of areas to which a motor is applied, for example such as areas of precision machines, household electrical appliances, and vehicles.